Patch "fs/select: add vmalloc fallback for select(2)" has been added to the 4.4-stable tree

Patch "fs/select: add vmalloc fallback for select(2)" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    fs/select: add vmalloc fallback for select(2)

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fs-select-add-vmalloc-fallback-for-select-2.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 2d19309cf86883f634a4f8ec55a54bda87db19bf Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Tue, 11 Oct 2016 13:51:14 -0700
Subject: fs/select: add vmalloc fallback for select(2)

From: Vlastimil Babka <vbabka@suse.cz>

commit 2d19309cf86883f634a4f8ec55a54bda87db19bf upstream.

The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows
with the number of fds passed. We had a customer report page allocation
failures of order-4 for this allocation. This is a costly order, so it might
easily fail, as the VM expects such allocation to have a lower-order fallback.

Such trivial fallback is vmalloc(), as the memory doesn't have to be physically
contiguous and the allocation is temporary for the duration of the syscall
only. There were some concerns, whether this would have negative impact on the
system by exposing vmalloc() to userspace. Although an excessive use of vmalloc
can cause some system wide performance issues - TLB flushes etc. - a large
order allocation is not for free either and an excessive reclaim/compaction can
have a similar effect. Also note that the size is effectively limited by
RLIMIT_NOFILE which defaults to 1024 on the systems I checked. That means the
bitmaps will fit well within single page and thus the vmalloc() fallback could
be only excercised for processes where root allows a higher limit.

Note that the poll(2) syscall seems to use a linked list of order-0 pages, so
it doesn't need this kind of fallback.

[eric.dumazet@gmail.com: fix failure path logic]
[akpm@linux-foundation.org: use proper type for size]
Link: http://lkml.kernel.org/r/20160927084536.5923-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/select.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- a/fs/select.c
+++ b/fs/select.c
@@ -29,6 +29,7 @@
 #include <linux/sched/rt.h>
 #include <linux/freezer.h>
 #include <net/busy_poll.h>
+#include <linux/vmalloc.h>
 
 #include <asm/uaccess.h>
 
@@ -550,7 +551,7 @@ int core_sys_select(int n, fd_set __user
 	fd_set_bits fds;
 	void *bits;
 	int ret, max_fds;
-	unsigned int size;
+	size_t size, alloc_size;
 	struct fdtable *fdt;
 	/* Allocate small arguments on the stack to save memory and be faster */
 	long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
@@ -577,7 +578,14 @@ int core_sys_select(int n, fd_set __user
 	if (size > sizeof(stack_fds) / 6) {
 		/* Not enough space in on-stack array; must use kmalloc */
 		ret = -ENOMEM;
-		bits = kmalloc(6 * size, GFP_KERNEL);
+		if (size > (SIZE_MAX / 6))
+			goto out_nofds;
+
+		alloc_size = 6 * size;
+		bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN);
+		if (!bits && alloc_size > PAGE_SIZE)
+			bits = vmalloc(alloc_size);
+
 		if (!bits)
 			goto out_nofds;
 	}
@@ -614,7 +622,7 @@ int core_sys_select(int n, fd_set __user
 
 out:
 	if (bits != stack_fds)
-		kfree(bits);
+		kvfree(bits);
 out_nofds:
 	return ret;
 }


Patches currently in stable-queue which might be from vbabka@suse.cz are

queue-4.4/fs-select-add-vmalloc-fallback-for-select-2.patch